In early July, an expedition of scientists and photographers traveled to Svalbard, an archipelago of islands in the Arctic Ocean about halfway between Norway and the North Pole. When they saw a polar bear on the shore from their boat, at first they weren't sure whether it was dead or alive.

A closer look onshore, however, revealed a shrunken, emaciated animal that likely starved and fell down, dying on the spot where it laid.

"It was very sad and very moving to see such a magnificent beast, the apex predator of the Arctic, reduced to little more than skin and bone," said Ashley Cooper, a U.K.-based photographer who traveled with the expedition and captured the images above, which are published on the website Global Warming Images.

While it is difficult to pinpoint the cause of the bear's death, the rapidly warming climate of the Arctic likely played a significant role by shrinking its hunting grounds, said Dr. Ian Stirling, a longtime polar bear researcher and professor at the University of Alberta who works with Polar Bears International and traveled with the expedition to Svalbard.

The bear was 16 years old and had been in good condition when it was captured just three months earlier by scientists from the Norwegian Polar Institute, he said in an email interview, adding that the bear also "had been captured in the same area in previous years, suggesting that a sudden movement so far from its normal range was unusual."

But most of the Svalbard fjords and inter-island channels – which freeze in winter to form the ice on which polar bears forage for their favorite food, ringed seals – did not freeze normally last winter, he explained, so many of the areas known as polar bear hunting grounds probably weren't as productive as past years.

"The bear likely went looking for food in another area but appears to have been unsuccessful," Stirling added. "From his lying position in death, the bear appears to simply have starved and died where he dropped."

Polar bears' diet consists almost exclusively of ringed seals, so they must hunt on sea ice to find enough food, notes Dr. Steven Amstrup, the chief scientist at Polar Bears International. But the period when sea ice is present in the Arctic is becoming shorter, which forces the bears to come ashore for longer stretches through the spring, summer and early fall.

"We have no evidence that they can forage successfully in open water or on land," he said, adding that studies of polar bears in Hudson Bay have shown they lose about two pounds of body weight for every day they're stranded on land. "And if you imagine losing almost two pounds of body weight a day, there's a limit to how long they can do that."

Worldwide, there are believed to be about 20,000 to 25,000 polar bears living in 19 population groups scattered throughout the Arctic, according to the science journal Nature Climate Change. Of these, eight are experiencing declining numbers, while three are stable and one (along the central northern Canadian coast) has actually increased, thanks to the persistence of summer sea ice.

Without the sea ice, some polar bears go into a kind of hibernation, which allows them to store fat reserves, while others swim out into open water for food. But that's proving more challenging with each passing year; off the coasts of Alaska and Russia, sea ice that once retreated about 30 miles in summer now retreats more than 300 miles away from land.

"The extra distance also means that any polar bears heading out to hunt have a long swim ahead of them," a report in Nature Climate Change notes. In a 2008 study, scientists tracked a bear that swam more than 420 miles over 232 straight hours -- more than nine days straight of swimming.

"Over the season she lost 22 percent of her body fat," the report added. "As well as her cub."